1. Technical Field
The present invention relates to an organic transistor, a method for producing an organic transistor, an electro-optical device, electronic equipment, etc.
2. Related Art
In recent years, organic transistors containing organic materials with electrical semiconduction (organic semiconductor materials) have been developed. For their suitability for reduction in thickness and weight, flexibility, low material cost, and other advantages, such organic transistors are expected to serve as switching elements in a flexible display or the like.
In such an organic transistor, an inorganic material may be used as a gate dielectric film material (see, e.g., JP-A-2003-86805). However, this impairs the flexibility, an advantage of an organic transistor, and thus is problematic. This also presents a process problem in that because a gas-phase process or a high-temperature heat-treatment is employed for forming the gate dielectric film, the formation of the gate dielectric film requires time and effort, cost, time, and the like. Further, in an organic transistor obtained by a method in which a gate dielectric film is formed after the formation of an organic semiconductor film, the organic semiconductor film may be deteriorated or degraded during the formation of the gate dielectric film. Therefore, it is generally difficult to achieve excellent transistor properties using a typical process that uses an inorganic material.
In order to avoid such inconveniences, as materials for forming a gate dielectric film, organic materials such as phenolic resin and acrylic resin are occasionally used, for example. However, these resins have high hygroscopicity, and generally cause the following problem. Specifically, when such an organic transistor is used in air, the gate dielectric film therein absorbs moisture, and the moisture content in the gate dielectric film is thus increased; this is likely to cause a shift of the threshold voltage (Vth), an increase in the gate leakage current, and dielectric breakdown. There also is an organic transistor in which a fluorine-containing polymer is used for a gate dielectric film or for the interface between a gate dielectric film and an organic semiconductor film (see, e.g., JP-A-2006-191115). Fluorine-containing polymers typically have low hygroscopicity. Therefore, an organic transistor that operates stably in air can be produced. Further, because fluorine is electronegative, in the state of being in contact with an organic semiconductor film, electrons emitted therefrom at the time of the formation of holes can be accommodated. This thus provides an advantage in that high carrier mobility can be achieved in an organic transistor where the carriers are holes. However, this may simultaneously cause an increase in the OFF current value. In such a case, a high ON/OFF ratio cannot be obtained, resulting in a decrease in the switching performance as a transistor.
Organic transistors having a gate dielectric film with a laminated structure have also been developed (see, e.g., JP-A-2007-150246 and JP-A-2008-172028). However, these disclosures relate to the control of the wettability of an organic semiconductor film or a gate dielectric film or to the inhibition of the degradation of the interface between an organic semiconductor film and a gate dielectric film. At present, no organic transistor with high carrier mobility, a high ON/OFF ratio, and practically stable operation in air has been established.